`hvplot.extension(compatibility)` does not work?

Firstly, I'm building on top of https://github.com/holoviz/holoviews/pull/6331 in order to get `holoviews.opts.defaults(backend)` to actually work. But then the `compatibility` does not seem to work anymore. Here's a MWE.

```python
import holoviews
import hvplot

hvplot.extension("bokeh", "matplotlib", compatibility="bokeh")

holoviews.opts.defaults(
holoviews.opts.Curve(
linewidth=1,
),
backend="matplotlib",
)
hvplot.output(backend="matplotlib")
curve = holoviews.Curve([0, 1, 2])
curve.opts(line_dash="dashed")
curve
```

After further debugging with this example, I couldn't get it to work in any combination. The version of `hvplot` I am working with is `0.10.0`